1. Field of the Invention
The invention relates to a coordinate reader. The coordinate reader comprises a coordinate input plate formed with coordinate input planes on both sides of the coordinate input plate which electrically reads X- and Y-coordinates of a coordinate input device on the coordinate input plate.
2. Description of the Prior Art
Japanese Laid-Open Patent Publication No. 59-14042 discloses a conventional coordinate reader, as illustrated in FIGS. 18A and 18B. FIGS. 18A and 18B illustrate a board B when coordinate input sheets B1 and B2 are in use, respectively. The board B is rotatable on a shaft AX, and has connectors CN1 and CN2 at a top and a bottom end thereof. Located within the board B are coils arrayed in the x-axis and y-axis for sensing coordinates (X, Y) of a stylus on the board B. The board B also has a connector CN that is connected to either the connector CN1 or CN2, and a control circuit CONT. As shown in FIG. 18A, the connector CN is connected with the connector CN1 when the sheet B1 is in use. The control circuit CONT recognizes that the sheet B1 is in use based on the output signal from the connector CN. In the same way, the connector CN is connected with the connector CN2, as shown in FIG. 18B, when the sheet B2 is in use. The control circuit CONT recognizes that the sheet B2 is in use based on the output signal from the connector CN. Then, the coordinates (X, Y) of the stylus are detected upon the output signal from the connector CN.
Japanese Patent Publication No. 60-29997 discloses another type of conventional coordinate reader. A board of the coordinate reader has input sheets on both sides of the board, and is rotatable on a shaft. The shaft is electrically connected to a bearing with a switching mechanism, thereby detecting the input sheet in use and detecting coordinates (X, Y) of a stylus.
As described above, the conventional coordinate readers use mechanical switches to recognize which of the coordinate input sheets is in use and to detect the coordinates (X, Y) of the stylus. However, when the contact of the mechanical switch is poor, the coordinate reader cannot recognize which coordinate input sheet is in use or sense the coordinates (X, Y) of the stylus.
In various exemplary embodiments of a coordinate reader that detects coordinates designated by alternating a magnetic field, the coordinate reader includes a base member with a plurality of first loop wires provided in a first surface of the base member, the first loop wires generating first signals in response to the alternating magnetic field induced from the coordinate input device, second loop wires provided in a second surface of the base member, the second loop wires generating second signals in response to the alternating magnetic field induced from the coordinate input device, a first input plane provided over the plurality of first loop wires; and a second input plane provided over the plurality of second loop wires; a signal detection unit that detects the first and the second signals; an input plane determination device that determines which of the first input plane or the second input plane the coordinate input device is placed on by using at least one of the first and the second signals; and a coordinate determination unit that determines first coordinates and second coordinates of the coordinate input device based on the detected first and second signals, respectively.
The strength of the magnetic field generated from the coordinate input device becomes lower with distance therefrom. The nearer the loop wires are to the coordinate input device, the larger the signals generated and detected on those loop wires. Therefore, the input plane determination unit can determine which of the first and second input planes the coordinate input device is placed on by using at least one of the detected signals and comparing the signal levels. Thus, the reliability of the coordinate reader in detecting the location of the coordinate input device and of sensing the coordinates of the coordinate input device is increased without the use of mechanical switches as found in conventional coordinate readers.
Further, the signal detection unit of the coordinate reader may comprise a first signal level detector that detects a first signal level and a second signal level detector that detects a second signal level, the first signal level being the levels of the signals that are generated on adjacent two first loop wires among the plurality of the first loop wires that are substantially equivalent, the second signal level being the levels of the signals that are generated on adjacent two second loop wires among the plurality of the second loop wires that are substantially equivalent.
The detected signal level varies depending on a position over the loop wires. In other words, the maximum signal level is detected at the center line of each of the loop wires, and the detected signal level becomes weaker as the position moves away from the center line of the loop wires. If the signal levels of different conditions are compared, the input plane determination device and the coordinate input plane will not determine the location of the coordinate input device. Hence, the input plane determination device determines which of the first input plane or the second input plane the coordinate input device is placed on by using at least one of the first signal level and the second signal level, thereby comparing the signal levels of the same condition to determine the location of the coordinate input device.
The coordinate reader may further comprise a correction unit that corrects at least one of the first coordinate and the second coordinate, upon the determination of the input plane by the input plane determination unit.
As mentioned above, the base member has the first and the second input planes. When the base member is turned over to an input plane after another input plane, the orientation of one of the first and the second loop wires is reversed. This causes the coordinate determination unit to determine the coordinate reversely. The coordinate corrector corrects and controls the coordinate determination unit to determine the coordinates accurately, without being reversed.